A centrifugal pump pertinent to the pump of the present invention is shown in U.S. Pat. No. 4,034,870. These centrifugal pumps are used to supply powders or granular materials, for example reactants or catalysts, to a space in which a pressure prevails which is higher than the external pressure. These pumps may of course also be used in situations where there is no pressure difference.
During operation of these pumps the solids are ejected through the supply tube into the rotating rotor.
As a result of the centrifugal acceleration the solid particles acquire a high velocity which enables them to overcome the pressure difference between the inside and outside of the vessel and to prevent leakage of gas from the pressurized vessel.
In some centrifugal pumps the rotor is provided with a number of radial passages termed centrifugal nozzles. In other models the solids may be hurled from the entire circumference of the rotor through a narrow slit which is confined by the edges of the two trays which together form the rotor. In that case it is also possible to allow the two discs to rotate with different velocities in order to prevent clogging of the slit.
The solid particles leave the rotor edge with a radial and a tangential velocity component. In the usual embodiments the rotor has a rotational speed of, for example, 500-5000 revolutions per minute and the particles acquire a radial velocity of approximately 10 m/s. In this way pressure differences of some tens of bars, for example, 20-40 bar may be overcome.
The pneumatic supply of finely divided solids from outside the vessel to the rotor is effected through a supply tube which, if desired, also forms the shaft or the axle of the rotor. The carrier gas which is generally at atmospheric pressure cannot be completely hurled into the vessel together with solids because the solid particles are so compressed at the edge of the rotor that little space is left between them. Were there to be a great deal of space, the gas would flow back from the pressurized vessel. Yet the carrier gas has to be withdrawn somehow from the rotor. To this end, use has so far been made of a discharge tube which is coaxially arranged within or around the supply tube. This discharge tube discharged the carrier gas countercurrently with the supply.
From the design point of view this was and is not a happy solution, particularly not if the diameters of the supply and discharge tube have to be increased in order to augment the throughput capacity. The diameters of the tubes may then become too large for low-friction bearings to be used. In addition, the bearing arrangement of two concentric tubes poses a problem in itself, as does the sealing against the high pressure prevailing in the vessel, the shielding of the bearings against solid particles and the fastening to the vessel wall or the rotor.